114 research outputs found
Absolute motions of globular clusters. II. [HST astrometry and VLT radial velocities in NGC6397]
In this paper we present a new, accurate determination of the three
components of the absolute space velocity of the Galactic globular cluster
NGC6397 (l 338d, b -12d). We used three HST/WFPC2 fields with multi-epoch
observations to obtain astrometric measurements of objects in three different
fields in this cluster. The identification of 33 background galaxies with sharp
nuclei allowed us to determine an absolute reference point and measure the
absolute proper motion of the cluster. The third component has been obtained
from radial velocities measured on spectra from the multi-fiber spectrograph
FLAMES at UT2-VLT. We find [mu_alpha cos(delta), mu_delta](J2000.0) = [+3.39
+/- 0.15, -17.55 +/- 0.15] mas/yr, and V_rad = +18.36 +/- 0.09 (+/-0.10) km/s.
Assuming a Galactic potential, we calculate the cluster orbit for various
assumed distances, and briefly discuss the implications.Comment: 7 pages, 5 figures, 4 tables. Accepted for publication in A&A, on
April 27 200
On the HI-Hole and AGB Stellar Population of the Sagittarius Dwarf Irregular Galaxy
Using two HST/ACS data-sets that are separated by ~2 years has allowed us to
derive the relative proper-motion for the Sagittarius dwarf irregular (SagDIG)
and reduce the heavy foreground Galactic contamination. The proper-motion
decontaminated SagDIG catalog provides a much clearer view of the young
red-supergiant and intermediate-age asymptotic giant branch populations. We
report the identification of 3 Milky Way carbon-rich dwarf stars, probably
belonging to the thin disk, and pointing to the high incidence of this class at
low Galactic latitudes. A sub-group of 4 oxygen-rich candidate stars depicts a
faint, red extension of the well-defined SagDIG carbon-rich sequence. The
origin of these oxygen-rich candidate stars remains unclear, reflecting the
uncertainty in the ratio of carbon/oxygen rich stars. SagDIG is also a gas-rich
galaxy characterized by a single large cavity in the gas disk (HI-hole), which
is offset by ~360 pc from the optical centre of the galaxy. We nonetheless
investigate the stellar feedback hypothesis by comparing the proper-motion
cleaned stellar populations within the HI-hole with appropriately selected
comparison regions, having higher HI densities external to the hole. The
comparison shows no significant differences. In particular, the centre of the
HI-hole (and the comparison regions) lack stellar populations younger than ~400
Myr, which are otherwise abundant in the inner body of the galaxy. We conclude
that there is no convincing evidence that the SagDIG HI-hole is the result of
stellar feedback, and that gravitational and thermal instabilities in the gas
are the most likely mechanism for its formation.Comment: Accepted for publication in A&A, 11 pages, 6 jpeg figure
The Galactic globular cluster NGC 1851: its dynamical and evolutionary properties
We have completely mapped the globular cluster NGC 1851 with VI CCD
photometry, obtaining a CMD for ca. 20500 stars. From the apparent luminosity
of the HB we derive a distance modulus (m-M)o=15.44+/-0.20. The presence of 7
"supra-HB" stars is confirmed. Six of them are identified as evolved
descendants from HB progenitors. Synthetic HR diagrams demonstrate that the
problem of the HB morphology could be solved by assuming a bimodal efficiency
of the mass loss along the RGB. We find evidence that the radial distribution
of the blue HB stars is different from that of the red HB and SGB stars. The
first measurement of the mean absolute I magnitude for 22 known RR Lyr
variables (=0.12+/-0.20 at [Fe/H]=-1.28), is given. We found 7 new RR Lyr
candidates (6 ab type and 1 c type), lowering the ratio N(c)/N(ab) to 0.38.
From a sample of 25 globular clusters (including NGC 1851) a new calibration
for DV(bump,HB) as a function of metallicity is derived, and we find some
evidence for an age-metallicity relation among GCs. We identify 13 blue
straggler stars, which do not show any sign of variability. The blue stragglers
are less concentrated than the SGB stars with similar magnitudes for r>80".
Finally, a radial dependence of the LF, a sign of mass segregation, is found.
Transforming the LF into a mass function and correcting for mass segregation by
means of multi-mass King-Michie models, we find a global MF exponent
x(0)=0.2+/-0.3.Comment: 19 pages, 5 figures, to be published in Astronomy & Astrophysics.
Appendices A and B are only available in electronic form at the CDS via
anonymous ftp to ftp://cdsarc.u-strasbg.fr or via
http://cdsweb.u-strasbg.fr/Abstract.htm
ESO Imaging survey: Optical Deep Public Survey
This paper presents new five passbands (UBVRI) optical wide-field imaging
data accumulated as part of the DEEP Public Survey (DPS) carried out as a
public survey by the ESO Imaging Survey (EIS) project. Out of the 3 square
degrees originally proposed, the survey covers 2.75 square degrees, in at least
one band (normally R), and 1.00 square degrees in five passbands. The median
seeing, as measured in the final stacked images, is 0.97", ranging from 0.75"
to 2.0". The median limiting magnitudes (AB system, 2" aperture, 5 sigma
detection limit) are U_(AB)=25.65, B_(AB)=25.54, V_(AB)=25.18, R_(AB) = 24.8
and I_(AB)=24.12 mag, consistent with those proposed in the original survey
design. The paper describes the observations and data reduction using the EIS
Data Reduction System and its associated EIS/MVM library. The quality of the
individual images were inspected, bad images discarded and the remaining used
to produce final image stacks in each passband, from which sources have been
extracted. Finally, the scientific quality of these final images and associated
catalogs was assessed qualitatively by visual inspection and quantitatively by
comparison of statistical measures derived from these data with those of other
authors as well as model predictions, and from direct comparison with the
results obtained from the reduction of the same dataset using an independent
(hands-on) software system. Finally to illustrate one application of this
survey, the results of a preliminary effort to identify sub-mJy radio sources
are reported. To the limiting magnitude reached in the R and I passbands the
success rate ranges from 66 to 81% (depending on the fields). These data are
publicly available at CDS.Comment: 24 pages, 26 figures. Accepted for pubblication in A&
The atrophic effect of 1,25(Oh)2 vitamin d3 (calcitriol) on c2c12 myotubes depends on oxidative stress
Dysfunctional mitochondrial metabolism has been linked to skeletal muscle loss in several physio-pathological states. Although it has been reported that vitamin D (VD) supports cellular redox homeostasis by maintaining normal mitochondrial functions, and VD deficiency often occurs in conditions associated with skeletal muscle loss, the efficacy of VD supplementation to overcome muscle wasting is debated. Investigations on the direct effects of VD metabolites on skeletal muscle using C2C12 myotubes have revealed an unexpected pro-atrophic activity of calcitriol (1,25VD), while its upstream metabolites cholecalciferol (VD3) and calcidiol (25VD) have anti-atrophic effects. Here, we investigated if the atrophic effects of 1,25VD on myotubes depend on its activity on mitochondrial metabolism. The impact of 1,25VD and its upstream metabolites VD3 and 25VD on mitochondria dynamics and the activity of C2C12 myotubes was evaluated by measuring mitochondrial content, architecture, metabolism, and reactive oxygen species (ROS) production. We found that 1,25VD induces atrophy through protein kinase C (PKC)-mediated ROS production, mainly of extramito-chondrial origin. Consistent with this, cotreatment with the antioxidant N-acetylcysteine (NAC), but not with the mitochondria-specific antioxidant mitoTEMPO, was sufficient to blunt the atrophic activity of 1,25VD. In contrast, VD3 and 25VD have antioxidant properties, suggesting that the efficacy of VD supplementation might result from the balance between atrophic pro-oxidant (1,25VD) and protective antioxidant (VD3 and 25VD) metabolites
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